In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting, and dielectric materials are deposited on or removed from a surface of a semiconductor wafer. Thin layers of conducting, semiconducting, and dielectric materials may be deposited by a number of deposition techniques. Common deposition techniques in modem processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and electrochemical plating (ECP).
As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization. Planarizing a surface, or “polishing” a surface, is a process where material is removed from the surface of the wafer to form a generally even, planar surface. Planarization is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. Planarization is also useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide an even surface for subsequent levels of metallization and processing.
Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize substrates such as semiconductor wafers. In conventional CMP, a wafer carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate urging the wafer against the polishing pad. The pad is moved (e.g., rotated) relative to the substrate by an external driving force. Simultaneously therewith, a chemical composition (“slurry”) or other fluid medium is flowed onto the substrate and between the wafer and the polishing pad. The wafer surface is thus polished by the chemical and mechanical action of the pad surface and slurry in a manner that selectively removes material from the substrate surface.
Conventional methods of manufacturing polishing pads include, for example, cast and skiving of mix polyurethane precursors and pore forming agents, impregnation and splitting of non-woven felt, and coating, coagulation and buffing on a modified non-woven felt. In addition, other methods for manufacturing polishing pads have been explored, including, photopolymerization of liquid precursors, net-shape molding, extrusion of thermo-formable polymers and sintering of polymeric powders (e.g., U.S. Pat. No. 6,017,265).
Sintering typically involves two or more thermoplastic polymers that are compacted under pressure, above the glass transition temperature. The mixture of the thermoplastics is place in a mold and exposed to the sintering condition. The end result is a pad with uniform dimensions and porosity. Unfortunately, the pad typically requires additional processing steps, such as, machining of grooves in order to create a functional pad. In addition, conventional sintering techniques are limited in forming polishing pads with varied porosity and material composition.
Accordingly, what is needed is a method of forming a polishing pad for chemical-mechanical planarization utilizing improved sintering techniques.